1. Field of the Invention
The invention relates to a scan device, and more particularly to a scan device including a pair of reflecting elements parallel disposed for reflecting light therebetween so as to increase a total optical path length.
2. Description of the Related Art
Conventional scan devices utilize a light source providing light for a document, and the light is reflected by the document to enter a reflecting unit including a plurality of reflecting elements. The reflecting elements reflect the light to an image sensor which converts the light into electronic signals. The electronic signals are further converted into a digital image by software.
Referring to FIG. 1, a conventional scan device is disclosed. The conventional scan device includes a carrier 150, a light source 160, a reflecting mirror 170, a first mirror 180, a second mirror 190, a third mirror 110, a fourth mirror 111, a fifth mirror 112, a lens 113 and a image sensor 114. Light emitted from the light source 160 is reflected by the reflecting mirror 170. The reflected light passes through a glass plate 140 to a document 130. The document 130 reflects the light into the carrier 150 to become a light beam L1. The light beam L1 is reflected to the second mirror 190 by the first mirror 180 to form a light beam L2. The light beam L2 is reflected to the third mirror L3 by the second mirror 190. The light beam L2 is further reflected by the third mirror 110 and the fourth mirror 111 to pass through a grating 115 and reach the fifth mirror 112. The light is reflected by the fifth mirror 112 to become a light beam L3 which passes through the lens 113 and forms an image on the image sensor 114. The fourth mirror 111 is disposed in the carrier 150 and positioned at an upper left corner by an angle of 45° with respect to the document 130. Light is reflected by the fourth mirror 111 and travels parallel to an axis to pass through the grating 115 and reach the fifth mirror 112. The fifth mirror 112 is disposed in the carrier 150 and positioned at a lower left corner by an angle of 45° with respect to the document 130. The light beam L3 is reflected by the fifth mirror 112 and enters the lens 113 and the image sensor 114. The described structure prevents undesired light from entering the lens 113 and the image sensor 114 through the fifth mirror 112 so as to avoid the light to overlap the image. In addition, the described structure can also decrease the total volume of the entire scan device.
As the scan device is developed to be more compact, it is an important object to have a better image quality even optical elements are disposed in a limited space. In a limited space, a total optical path length is increased by adding more reflecting elements, which increases a depth of field to obtain better image quality even for a document with folds. In addition, the undesired light is prevented to enter the lens to overlap the image formed on the image sensor.